1. Field of the Invention
The present invention relates to a nuclear magnetic resonance spectrometer, and more particularly to a Fourier transform nuclear magnetic resonance spectrometer (hereinafter referred to as an FT-NMR spectrometer) in which a high frequency pulse is applied to a sample placed in a magnetic field, and a free induction decay signal (hereinafter referred to as an FID signal) of a nuclear spin resulting from the application of the high frequency pulse is Fourier-transformed to obtain a frequency spectrum.
2. Description of the Prior Art
Although atomic nuclei of hydrogen (.sup.1 H), carbon (.sup.13 C), fluorine (.sup.19 F) , or the like can be measured with the nuclear magnetic resonance spectrometer, the conventional FT-NMR spectrometer has been used mainly to measure .sup.13 C. Since .sup.13 C is about 1% in natural abundance ratio and is contained in a sample in a very small quantity as compared with hydrogen or the like, a resonance signal of .sup.13 C detected by a nuclear magnetic resonance spectrometer is very weak. Accordingly, as is disclosed in U.S. Pat. No. 3,475,680, signal detection is conducted scores of times in a short time with the FT-NMR spectrometer, and the detected signals are added to improve the signal-to-noise ratio. With respect to .sup.13 C, however, there is utilized the chemical shift appearing in a frequency spectrum.
A regards .sup.1 H, both the chemical shift and the signal strength in the frequency spectrum have been measured recently to effect the structural analysis of low molecular weight materials. Thus, it is required to measure the strength of the signal with a high accuracy. Although .sup.1 H can be measured with a general frequency-sweep or field-sweep nuclear magnetic resonance spectrometer because of its signal strength greater than that of .sup.13 C, the measurement of .sup.1 H with the FT-NMR spectrometer is effective in that the measuring time can be shortened, or when a sample of a very small-amount which is extracted in synthesizing a compound or the like, has to be dealt with. However, the conventional FT-NMR spectrometer has a drawback that the signal strength cannot be measured with high accuracy for atomic nuclei, for example, .sup.1 H which requires a highly accurate measurement of signal strength.